1. Technical Field of the Invention
The present invention relates to channel and network communication systems and processes and, in particular, to a system and method for controlling multiple initiators in a Fibre Channel environment.
2. Description of Related Art
There are two kinds of protocols for device communication: channels and networks. Channels, between a master host computer and a slave peripheral device, are designed to transport a large amount of data at very high speeds over relatively small distances with little software overhead once data transmission commences. A channel generally provides a direct or switched point-to-point connection between a master and a slave that is hardware-intensive. Networks, on the other hand, are designed to interface many users, sharing a plurality of hosts and system resources, over medium to large distances and support many transactions. With respect to networks, higher overhead is generally acceptable as long as high connectivity is achieved.
The Fibre Channel Protocol ("FCP") is a new generation protocol that combines the best of these two disparate methods of communication in a single Open-Systems-Interface-like (OSI-like) stack architecture. Essentially, the Fibre Channel ("FC") is a multi-topology, multi-layer stack with lower-layer-protocols ("LLPs") for controlling the physical transport characteristics and upper-layer-protocols ("ULPs") for mapping LLP communication to and from higher-level software structures that are compatible with an Operating System. These ULPs include both channel and network protocols such as Intelligent Peripheral Interface ("IPI"), Small Computer System Interface ("SCSI"), and Internet Protocol ("IP"), among others.
It is well-known that devices that engage in either channel or network communication may be categorized as "initiators" or "targets" or both, depending upon their functionality. Certain specific functions are assigned to either an initiator or a target: (i) an initiator can arbitrate for the communication path and select a target; (ii) a target can request the transfer of command, data, status, or other information to or from the initiator, and (iii) in some instances, a target can arbitrate for the communication path and reselect an initiator to continue a transaction.
For devices that are operable with the Fibre Channel Protocol, only those devices which have the initiator functionality may initiate what is known in the art as a Link Service Request or an Extended Link Service Request. Link Service commands provide Fibre Channel initiators with the ability to perform such tasks as Node Discovery, Abort Requests and Reject Communication frames. The only Link Service command a Fibre Channel target can initiate is a Reject command/frame ("LS.sub.-- RJT").
Typically, in a single initiator FC environment, the initiator device sends out such Link Service Commands as are needed and expects in response thereto an Acknowledgment ("LS.sub.-- ACK") frame or a Reject frame (LS.sub.-- RJT) from a target. Hereinafter, these LS.sub.-- ACK and LS.sub.-- RJT frames will be collectively referred to as "response" frames. In a multi-initiator environment, on the other hand, an initiator operates as both a recipient and a sender of Link Service commands. Because of these twin roles, such an initiator operates as both a recipient and a sender of a response frame.
It is known in the art that because of these bi-directional transmissions among the initiators, there is a great potential for severe confusion in a multi-initiator FC environment. In fact, due to such confusion on the part of initiators, initialization procedures responsible for establishing a viable communication link have been known to stall, causing transmission interruptions in multi-initiator environments.
It can be appreciated that although providing multiple initiators in a channel or network communication system would conceptually increase performance levels and achieve a higher degree of connectivity, interruptions such as those described above in a multi-initiator FC environment could also increase the down-time for the communication links to unacceptable levels in high-performance, leading-edge systems.
Although various single initiator FC implementations have been extant for some time, no multi-initiator FC communication system is known that adequately addresses the above-described problems and deficiencies and/or possesses all of the advantages and novel features of the invention described and claimed hereinbelow.